FIG. 3 is an exploded perspective view of a conventional semiconductor pressure sensor device illustrated in FIG. 1 of Japanese Patent No. 4281178 (Patent Document 1). FIG. 4 is a sectional view of the conventional semiconductor pressure sensor device illustrated in FIG. 2 of Patent Document 1. The conventional semiconductor pressure sensor device includes a first case 20, leads 30, a second case 40, and a surrounding portion 42. The first case 20 is molded from a resin. A sensor element constituted of a semiconductor is disposed in the first case 20. The leads 30 are insert-molded in the first case 20 such that the leads 30 are partially exposed from the first case 20, and exposed portions thereof are electrically connected to the sensor element. The second case 40 is assembled with the first case 20 to cover the sensor element. The surrounding portion 42 is formed on the second case 40 to surround the exposed portions of the leads 30. The exposed portions of the leads 30 and the surrounding portion constitute a connector portion that enables the exposed portions of the leads 30 to be connected to external terminals. The first case 20 and the second case 40 slide to fit with each other. An engagement structure (25, 47) is provided between the first case 20 and the second case 40 for preventing disengagement of the first and second cases. The first case 20 is integrally provided with a cylindrical body 21 into which a fluid to be measured flows.
As illustrated in FIG. 4, the sensor case 20 has an opening portion 20a on one side thereof. A sensor element 10 etc. is disposed in the opening portion 20a. The sensor case 20 also has a pressure introduction port 21 configured to project toward the opposite side from the bottom surface of the opening portion 20a. The distal end portion of the pressure introduction port 21 is mountable at an appropriate location of a flow path in a hot water supply device via an O-ring or the like. An introduction hole 22 is provided inside the pressure introduction port 21 to introduce a pressure from the flow path.
The bottom surface of the opening portion 20a of the sensor case 20 is formed with a recessed portion 23 recessed from a flat portion of the bottom surface. The sensor element 10 is fixed in the recessed portion 23 via a base 11 made of glass or the like. The sensor element 10 is configured such that a plurality of diffused resistors are formed on a diaphragm made of a semiconductor material (e.g. monocrystalline silicon) having a piezoresistance effect and connected to each other by bridge connection, although not illustrated. Variations in resistance value of the diffused resistors according to deformation of the diaphragm are taken out from the bridge circuit as an electrical signal.
The sensor element 10 and the base 11 are bonded to each other by glass bonding or the like. A through hole that communicates with the introduction hole 22 is formed inside the base 11. A pressure from the flow path is transmitted from the introduction hole 22 to the diaphragm of the sensor element 10 through the through hole of the base 11. The recessed portion 23 is filled with a sealing agent 24 in order to enhance the air-tightness between the through hole of the glass base 11 and the introduction hole 22.
A bipolar transistor element 12 and a MOS transistor element 13 are fixed in the opening portion 20a of the sensor case 20 by an adhesive or the like. The bipolar transistor element 12 serves as an amplification circuit operable to amplify an output signal from the sensor element 10. The MOS transistor element 13 serves as an adjustment circuit operable to adjust the output signal from the sensor element 10, a signal from the bipolar transistor element 12, etc.
The sensor element 10, the bipolar transistor element 12, the MOS transistor element 13, and the leads 30 are electrically connected to each other, as appropriate, by a plurality of wires 14 formed by wire bonding and made of gold, aluminum, or the like. The electrical signal (output) from the sensor element 10 is taken out from each of the elements 12 and 13, the leads 30, and exposed portions 31 of the leads 30 through the wires 14.